Clinical value of specific detection of immune complex-bound antibodies in pulmonary tuberculosis

Mycobacterium tuberculosis Cell Wall Antigens Induce the Formation of Immune Complexes and the Development of Vasculitis in an Experimental Murine Model

Tuberculosis (TB) of the central nervous system (CNS) presents high mortality due to brain damage and inflammation events. The formation and deposition of immune complexes (ICs) in the brain microvasculature during Mycobacterium tuberculosis (Mtb) infection are crucial for its pathobiology. The relevance of ICs to Mtb antigens in the pathogenesis of CNS-TB has been poorly explored. Here, we aimed to establish a murine experimental model of ICs-mediated brain vasculitis induced by cell wall antigens of Mtb. We administered a cell wall extract of the prototype pathogenic Mtb strain H37Rv to male BALB/c mice by subcutaneous and intravenous routes. Serum concentration and deposition of ICs onto blood vessels were determined by polyethylene glycol precipitation, ELISA, and immunofluorescence. Histopathological changes in the brain, lung, spleen, liver, and kidney were evaluated by hematoxylin and eosin staining. Our results evidenced that vasculitis developed in the studied tissues. High serum levels of ICs and vascular deposition were evident in the brain, lung, and kidneys early after the last cell wall antigen administration. Cell wall Mtb antigens induce strong type III hypersensitivity reactions and the development of systemic vasculitis with brain vascular changes and meningitis, supporting a role for ICs in the pathogenesis of TB.

Tuberculosis-associated IgA nephropathy

Immunoglobulin A nephropathy (IgAN) is the most frequent pathological diagnosis of tuberculosis (TB)-associated glomerulonephritis. Diagnosing TB-associated IgAN (TB-IgAN) is difficult because of its non-specific and insidious symptoms. An inaccurate diagnosis of TB-IgAN could result in the spread of TB and reduced renal function. Haematuria and proteinuria in conjunction with TB should be assessed because of the potential for diagnosis of IgAN. Renal biopsy is important in securing an accurate diagnosis prior to initiating treatment. Detection of Mycobacterium tuberculosis DNA and assessment of early secreted antigenic target of 6 kDa in renal biopsy tissues may have great potential diagnostic value in patients with TB-IgAN. Anti-TB therapy can effectively alleviate TB and TB-IgAN.

Glycoproteins in circulating immune complexes are biomarkers of patients with Indian PKDL: A study from endemic districts of West Bengal, India

BACKGROUND

Post Kala Azar Dermal Leishmaniasis (PKDL) occurs as dermal consequence of previous Visceral Leishmaniasis (VL) infection and serves as an important reservoir for transmission of VL. Diagnosis of PKDL is often challenging for its symptomatic resemblance to other co-endemic diseases like Leprosy or Vitiligo. Parasitological examination by slit-skin smear and culture are the standard methods but lack high sensitivity. Thus, for efficient control of VL, reliable diagnostic and prognostic assay of PKDL are required.

OBJECTIVE

Previously, glycoproteins (9-OAcSA) have been reported as promising biomarkers of Indian VL patients. However, till date, the status of glycans in Indian PKDL patients remains unexplored. Accordingly, in this study, the glyco-profile of PKDL Circulating Immune Complexes (CICs) as compared to other cross diseases like Vitiligo and Leprosyhas been investigated. Further, a novel Glyco CIC assay has been developed for efficient Indian PKDL patient diagnosis.

METHODS/PRINCIPAL FINDING

In the present study, 90 PKDL patients were enrolled from 3 VL endemic districts of West Bengal during 2015-16. Glycosylation profile of isolated CICs from sera of PKDL patients were initially analyzed through gradient SDS gel electrophoresis followed by PAS silver double staining, which revealed the presence of several glycan rich PKDL specific proteins of varying molecular weights. To further characterize the glyco-profile of acid dissociated affinity purified immuno-reactive antigens present in the CICs, glycosylation was demonstrated in these purified CIC antigens by DIG glycan differentiation kit with or without glycosidase as well as neuraminidase treatment. Diagnostic evaluation of the newly developed colorimetric Glyco CIC assay through Receiver Operating Characteristic (ROC) curve analysis revealed excellent (0.99) AUC value as compared to other conventional serodiagnostic assays like PEG CIC, Parasite ELISA (IgG and IgM). Additionally, longitudinal monitoring of 18 PKDL patients further revealed its good prognostic utility.

CONCLUSION

These results highlight the glycosylation status of CICs among Indian PKDL patients present in all the studied endemic districts of West Bengal. These PKDL biomarkers were completely absent in cross diseases like Vitiligo and Leprosy. Further, the newly developed Glyco CIC assay had an improved sensitivity of 95.6%, specificity of 99.3%, NPV of 97.1% and PPV of 98.9%.

Complement pathway gene activation and rising circulating immune complexes characterize early disease in HIV-associated tuberculosis

The transition between latent and active tuberculosis (TB) occurs before symptom onset. Better understanding of the early events in subclinical disease will facilitate the development of diagnostics and interventions that improve TB control. This is particularly relevant in the context of HIV-1 coinfection where progression of TB is more likely. In a recent study using [¹⁸F]-fluoro-2-deoxy-d-glucose positron emission/computed tomography (FDG-PET/CT) on 35 asymptomatic, HIV-1-infected adults, we identified 10 participants with radiographic evidence of subclinical disease, significantly more likely to progress than the 25 participants without. To gain insight into the biological events in early disease, we performed blood-based whole genome transcriptomic analysis on these participants and 15 active patients with TB. We found transcripts representing the classical complement pathway and Fcγ receptor 1 overabundant from subclinical stages of disease. Levels of circulating immune (antibody/antigen) complexes also increased in subclinical disease and were highly correlated with C1q transcript abundance. To validate our findings, we analyzed transcriptomic data from a publicly available dataset where samples were available in the 2 y before TB disease presentation. Transcripts representing the classical complement pathway and Fcγ receptor 1 were also differentially expressed in the 12 mo before disease presentation. Our results indicate that levels of antibody/antigen complexes increase early in disease, associated with increased gene expression of C1q and Fcγ receptors that bind them. Understanding the role this plays in disease progression may facilitate development of interventions that prevent this, leading to a more favorable outcome and may also be important to diagnostic development.

Elucidating the interplay between IgG-Fc valency and FcγR activation for the design of immune complex inhibitors

Autoantibody immune complex (IC) activation of Fcγ receptors (FcγRs) is a common pathogenic hallmark of multiple autoimmune diseases. Given that the IC structural features that elicit FcγR activation are poorly understood and the FcγR system is highly complex, few therapeutics can directly block these processes without inadvertently activating the FcγR system. To address these issues, the structure activity relationships of an engineered panel of multivalent Fc constructs were evaluated using sensitive FcγR binding and signaling cellular assays. These studies identified an Fc valency with avid binding to FcγRs but without activation of immune cell effector functions. These observations directed the design of a potent trivalent immunoglobulin G-Fc molecule that broadly inhibited IC-driven processes in a variety of immune cells expressing FcγRs. The Fc trimer, Fc3Y, was highly efficacious in three different animal models of autoimmune diseases. This recombinant molecule may represent an effective therapeutic candidate for FcγR-mediated autoimmune diseases.

Pesquisa de IgA contra o antígeno recombinante HspX de Mycobacterium tuberculosis no diagnóstico de tuberculose pleural

OBJETIVO: Avaliar a acurácia da dosagem de IgA contra o antígeno recombinante HspX no líquido pleural e no soro de pacientes com derrame pleural para o diagnóstico de tuberculose pleural. MÉTODOS: Estudo transversal de teste diagnóstico. Amostras de líquido pleural e de soro de pacientes com derrame pleural e suspeita de tuberculose pleural foram avaliadas para a determinação da densidade óptica de IgA contra HspX utilizando ELISA indireto. RESULTADOS: Foram avaliadas amostras de líquido pleural e de soro de 132 pacientes: 97 com tuberculose pleural (grupo de estudo) e 35 com derrame pleural por outras causas (grupo controle). A dosagem de IgA em líquido pleural foi capaz de discriminar os pacientes com tuberculose pleural dos controles. A sensibilidade do teste em líquido pleural e em soro foi, respectivamente, de 69% e 30%, enquanto a especificidade foi de 83% e 84%, respectivamente. CONCLUSÕES: Os dados sugerem o potencial da utilização deste teste no diagnóstico de tuberculose pleural. Estudos com amostras maiores e em diferentes cenários epidemiológicos são necessários

Assessment of three commercially available serologic assays for detection of antibodies to Mycobacterium tuberculosis and identification of active tuberculosis

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a major world disease, with approximately 9 million new cases each year. Identification and treatment of active disease are essential for TB control. Serology may offer increased detection of active disease in patients with a positive tuberculin skin test (TST) or QuantiFERON-TB (QFT-G). The InBios Active TbDetect immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA), IBL M. tuberculosis IgG ELISA, and Anda Biologics TB ELISAs were evaluated for the ability to detect M. tuberculosis antibodies in patients with active disease. Agreement, sensitivity, and specificity for each ELISA were determined and compared to those for culture or amplified direct detection and M. tuberculosis low-risk control patients. The InBios Active TbDetect ELISA had an agreement of 96.2%, a sensitivity of 83.3%, and a specificity of 98.9%. The IBL M. tuberculosis ELISA had an agreement of 84.0%, a sensitivity of 5.6%, and a specificity of 100.0%. The agreement, sensitivity, and specificity of the Anda Biologics TB ELISA were 74.2%, 83.3%, and 72.0%, respectively. The sensitivity for detecting M. tuberculosis antibodies in human immunodeficiency virus-associated TB was 50% for both the InBios Active TbDetect ELISA and the Anda Biologics TB ELISA and 0% for the IBL M. tuberculosis ELISA. The positivity rates for InBios Active TbDetect ELISA, IBL M. tuberculosis ELISA, and Anda Biologics TB ELISA in latently infected individuals positive by TST and/or QFT-G were 5.1%, 0.0%, and 30.8%, respectively. It can be concluded that the InBios Active TbDetect IgG ELISA is superior to the other ELISAs in accurately detecting active TB.

McNemar chi2 test revisited: comparing sensitivity and specificity of diagnostic examinations

When evaluating a novel diagnostic examination for clinical use, it should be compared with a reference standard, defined as the best available examination, which may include clinical and laboratory criteria. The novel examination and reference standard's results are usually presented in the form of a 2 x 2 table, which allows calculation of sensitivity, specificity and accuracy. It has been recommended that the measures of statistical uncertainty should be reported, such as the 95% confidence interval, when evaluating the accuracy of diagnostic examinations. Comparing the difference in sensitivity or specificity of a novel examination with the reference standard is important when evaluating its usefulness. The McNemar chi(2) test, used to compare discordance of two dichotomous responses, can be applied for this purpose. However, applying the McNemar test to a 2 x 2 table for comparing the accuracy of examinations is not recommended, since this test is sensitive to the proportion of positive versus negative subjects. Moreover, if the novel examination has higher sensitivity than the one considered as the reference standard, constructing a classic 2 x 2 table would result in low specificity of the novel examination. Thus, in order to compare sensitivities and specificities between examinations, this table is inappropriate and an independent reference standard is necessary. In this article, we propose the use of the McNemar chi(2) test to compare sensitivities between examinations using a 2 x 2 table exclusively among diseased patients, defined by a set of criteria and follow-up of patients. Likewise, specificities can be compared applying the McNemar test among healthy individuals.